What are the advantages to a Class A amp & what are the trade offs?


I've never had a class a amp but am considering one now. So what am I getting myself into?
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Use of class A allows achieve low distortion with less feedback applied. That is the main advantage. Main problem is the heat: at full power amplifier will convert into heat 3 times more energy than it sends to speakers. At zero output power energy that is not sent to speaker is converted into heat too.
From 1980 - 2019, Classe' Audio's DR-3 is still the sweetest amp I've heard. It just didn't work in my 25x15 room.
So what does that say for class A amps?
That said, I have not heard Threshold's SA12, or Pass Labs xs300.
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Class A may well have been superceded by other topologies. Even some chip gaincones sound very good. 
Sugden have made and continue to make, Class A amps. They're handmade in the UK. 
My introduction, as a musician, to class A was an epiphany. 
I built and listened to commercial class B amps at university.
I performed in a concert in a church with a large organ in 1974.
The concert was recorded. 
On playback the revelation was how every upper rank of the organ was crystal clear. There was no blurring I'd been accustomed to with other amplifiers.
My main instruments of study were piano and flute but I played a lot on pipe organ.
That was my epiphany. 
I've listened to a DIY Sugden 10w class A driving Lowther speakers. 
My degrees and diplomas are in classical music. 
I spent 30 yrs producing recordings of concerts for broadcast on national radio. 
We used proper commercial equipment with standard Neumann, b&k and akg microphones. 
My class A + Lowther combo was used as a reference. If the recording sounded good on them, then it was fine on anything. 
Our studios used B&W and Tannoy monitors, but most recordings were made in our mobile van.